Where do I set the sensor ID?

I am going to use openHAB as my controller and as for as I can tell I need to manually set sensor IDs for each bit of kit in my network. I am using a serial gateway, well, was but am currently faultfinding it, and I have a motion sensor that seems to have picked up id 105, I am assuming from the sketch. I can't find 105 anywhere in the sketch for the moion sensor so where is this likely to have come from and how do I set the id for other sensors?
Cheers

@mfalkvidd
Thanks! I have now set a value of 1 and lo and behold sensor 1 is now talking to the gateway. I vaguely remeber testing eeprom storing values by using a button that advanced a value by one and then stored it. It must have been this Uno I did it on and I must have hit the button 105 times